Evaluation of MAPK and PI3K/AKT Signaling Pathways In Adult Acute Lymphoblastic Leukemia

Treatment of adult acute lymphoblastic leukemia (ALL) has shown only modest improvements over the last 2 decades, with overall survival of 15% to 40%. The mitogen-activated protein kinase (MAPK) signaling cascade and the phosphoinosytol-3 phosphate/AKT (PI3K/AKT) pathways are involved in proliferation and differentiation of hematopoietic cells. It has been reported that those pathways are frequently activated in solid tumors and acute myeloid leukemia. However, their role in adult ALL is still uncertain. Better understanding of such pathways is necessary for development of novel therapeutic strategies.

To evaluate the phopho-ERK and phospho-AKT protein expression in ALL at diagnosis and to correlate with biological and clinical parameters.

Twenty eight patients (median age 33y, 14–69y) with ALL at diagnosis were studied. Bone marrow and/or peripheral blood mononuclear cells (PBMC) (10 fresh and 18 cryopreserved cells at diagnosis) were stained using phospho-ERK and phospho-AKT/alexafluor 488 monoclonal antibodies (Cell Signaling Technology, Beverly, MA) and their expression was evaluated by flow cytometry (FACScalibur cytometer and CELL Quest program - BDB, San Jose, CA). The monoclonal antibodies CD19, CD10, CD3, CD45, IgM, CD34, CD7, CD2 were used for leukemic cells characterization by four-colour staining. Healthy donor PBMC and Jurkat cell line were used as controls: normal T lymphocytes are negative for p-ERK and Jurkat cell line express p-ERK and p-AKT in low levels. Samples were analyzed for constitutive expression of p-ERK and p-AKT and also after cell activation by phorbol-myristate-acetate (PMA). The expression of these proteins was evaluated by Kolmogorov-Smirnov test using fluorescence ratio between control isotype and phospho-protein (D). p-ERK and p-AKT expression was also evaluated in fresh and frozen samples of the same patients (2 cases) and similar results were obtained. In addition, patients were evaluated for multidrug resistance (MDR) through p-glycoprotein (PGP) expression and Rhodamine (Rh) efflux test and minimal residual disease (MRD) detection at the end of induction by flow cytometry.

Twenty cases were B-ALL (EGIL B-I 3, B-II 9, B-III 8, B-IV 5) and 3 T-ALL. Median WBC count was 25.3×10⁹/L (2.3-373×10⁹/L). The expression of p-ERK and p-AKT varied and the median value of p-ERK expression was D = 0.16 (0.01-0.80) and p-AKT median D = 0.08 (0.00-0.63). Considering these values as cutoff there was no difference regarding the patients` age and WBC count at the diagnosis between the positive and negative groups. In regards to EGIL subtypes, p-ERK expression was higher in T-ALL [median 0.50 (0.18-0.54)] than in B-precursor ALL [median 0.14 (0.01-0.80)] (p=0.03). Conversely p-AKT expression was similar in all cases, although high levels were observed among BIII cases. The frequency of Rh efflux was 88% in pERK negative cases and 66% in positive group but there was no difference on PGP expression. On the contrary, PGP expression and Rh efflux were more frequently seen in p-AKT positive cases (88% and 100%, respectively) than p-AKT negative ones (63% and 60%). MRD analysis was performed in seven patients. Two cases presented detectable MRD (>0.01%) and both were p-ERK positive and p-AKT negative. Interestingly all five MRD (-) cases were p-ERK negative and p-AKT positive. In addition, PMA test showed p-ERK activation of normal T lymphocytes and the expression was increased in 52% of ALL cases upon treatment.

MAPK and PI3/AKT activation varied among ALL patients. MAPK pathway showed to be more activated in T-ALL than in precursor-B ALL. The functional analysis of these pathways can address the role in ALL pathogenesis. Both pathways may be potential therapeutic targets for novel therapies. (Support: FAPESP proc.09/51002-8).

No relevant conflicts of interest to declare.